The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Referring now to FIG. 1, a functional block diagram of a battery pack 100 according to the prior art is presented. The battery pack 100 includes multiple cells 106-1, 106-2, 106-3, and 106-4, each having a positive and a negative terminal. The cells 106 are connected in series, with the positive terminal of one of the cells 106 connected to the negative terminal of a next one of the cells 106. In various implementations, the cells 106 may be lithium ion (LiIon) charge storage cells.
The negative terminal of the cell 106-4 is connected to an external contact, which may interface with a power tool or a charger. The positive terminal of the cell 106-1 is connected to a switch 110. When the switch 110 is conducting, the positive terminal of the cell 106-1 is connected to an external contact, which may interface with the power tool or the charger. The switch 110 is controlled by a protection system 114. The protection system 114 monitors voltages at the positive and negative terminals of each of the cells 106.
The cells 106 may have varying charge storage capacities. The cells 106 with lower charge storage capacities will decrease in voltage faster than the cells 106 with larger storage capacities. The protection system 114 measures the voltages of the cells 106 and instructs the switch 110 to stop conducting when the voltage of one of the cells becomes too low. In addition, the switch 110 may stop conducting if the current flowing through it exceeds a safe operating level.